INFRASOUND – why it matters
Infrasound is sound that is below the threshold of human hearing. The figure to the right shows the frequency (or tone) for average humans when they talk, compared to a forest elephant rumble. Humans with very good hearing can just barely detect sounds at 20 Hz, but part of a typical elephant rumble is below 20 Hz, so humans can’t hear that.
Infrasound matters because low-frequency sound generally travels farther through closed habitats than higher-frequency sound. Forest elephants, who spend the majority of their lives hidden within the closed-canopy forests of Central Africa, exploit this characteristic when they talk to one another using very low frequency calls known as ‘rumbles’. Whether their family groups are separated by kilometers of forest, or males are searching for females in estrous, rumbles built on a fundamental frequency in the infrasonic range can be heard over long distances, and we can eavesdrop on these conversations using recorders. The simple animation below shows the basics of this relationship.
The Elephant Listening Project records and analyzes forest elephant calls to better understand where they are, what they’re doing, and what they’re trying to tell us. The pages below delve deeper into infrasound, the part it plays in elephant communication, and how we study it.